Type 2 (or EN61643 Class II) protection devices are designed to protect installations where a direct strike is unlikely to occur. Buildings that do not require structural lightning protection or buildings in low lightning regions are much less likely to receive a direct strike to the point of power entry on the building. Type 2 surge protection is required as secondary protection downstream of spark gap based Type 1 protection.
Find Type 2 Power Protection by Novaris here.
The waveform that simulates the attenuated indirect strike or switching surges is the 8/20µs current impulse. 8µs is the length of time required to reach 90% of the maximum current and 20µs is the length of time for the current flow to fall back to 50% of maximum. The 8/20µs waveform represents the majority of surges that a power system will be exposed to.
The Metal Oxide Varistor’s (MOV) electrical properties are similar to those of a semiconductor. The component is in a high impedance state when a voltage lower than the ‘clamping voltage’ rating is applied. The component instantaneously changes to a low impedance state when the ‘clamping voltage’ is exceeded. This re-directs a majority of the surge current away from the load whilst reducing the surge voltage exposure. The advantages of MOV technology are its lower residual voltage (Up), instantaneous reaction time and no follow on current (Ifi) that can cause circuit breakers tripping.
Novaris Type 2 surge protection devices utilise active alarm technology. This technology requires power from the incoming phases to activate the LED indication and alarm relay within the device. The advantage of active monitoring is that the alarms respond to multiple failures that could impede the surge protection installation.
- Surge component monitoring: If a MOV segment degrades the segment LED will turn off and change the alarm state, alerting the operator that the device needs to be replaced.
- HRC fuse monitoring: A large surge or a short circuit failure of the MOV can cause the protection fuse to blow. The alarm monitors the continuity of the fuse which in turn monitors the SPDs connection to the circuit.
- Phase failure monitoring: The alarm and indication will change state in the case of a phase failure which can suggest a loose connection or a more serious fault upstream.
During a surge the Metal Oxide Varistor (MOV) components change to a low impedance state to pass the surge current. The combination of this current and the residual MOV resistance can generate a substantial amount of heat. Additionally, temporary over voltages can cause the MOVs to fail to a low impedance state where they start to conduct AC current, which also generates heat. To reduce the risk of heat damage from failed MOVs, Novaris Type 2 surge protection devices are housed in metal enclosures. This reduces the instantaneous heat exposure and diminishes the risk of burning.